Air compressors and vacuum pumps are typically oil sealed or lubricated and thus compressors and pumps generate a heavy concentration of oil both in the form of oil vapor and oil-mist particles in the exhaust air during the pumping cycles. Typically the oil-mist droplets are very small, often well below 5 microns in average size. The oil mist, which is mostly composed of finely divided liquid droplets dispersed in air and visible typically as a haze, a fog, and the droplet size represent a health hazard in the environmental working place. Typically such oil mist is removed by employing a suitable filter, such as a glass-fiber filter, which removes the oil mist by a process of coalescing that permits the coalesced oil to drain from the filter.
There is a need for a means of testing on an easy semiquantitative basis the amount of oil mist in compressed air in order to determine the type and nature of the filters to employ in the compressed-air line. Present techniques to determine the amount of oil mist in compressed air are often quite cumbersome, expensive, complex or tedious. Such present techniques include the sampling of air from the compressed-air line, which air sample is then subject to test by a gas chromatograph, a mass spectrometer or hydrocarbon analyzer to determine the amount of oil in the air. However, such techniques ofter measure not only the oil-mist particles captured by the glass-fiber filter, but also the oil vapor in the air and in addition such tests do not provide for the testing of the compressed air under operating-line conditions and pressure. Such test methods also represent problems in getting an accurate representative sample of the compressed air, particularly where the oil-mist particles are so small and therefore, there are problems associated with the isokinetic sampling of compressed air.
One test method in use is a modification of a DRAEGER tube wherein a glass tube is filled with a selective oil absorbent and the gas to be tested is then passed through the tube. The absorbent contains a visual color indicator and the change in color and the intensity of the color change are observed as an indication of the presence of a particular gas. This test is typically employed for toxic gases, such as hydrogen sulfide, rather than for oil mist from compressed air or vacuum pumps. In the test modification oil absorbent with a color indicator is employed in a tube and compressed air bled through the tube at a known flow rate and the color change observed as an indication of oil mist in the air. This test is still quite insensitive, since the amount of air flow depends on the line pressure and the time factor involved in the test. In summary the present mentods and related techniques to determine oil-mist particles in a compressed-air stream are quite limited, insensitive, complex, expensive, tedious, hard to perform and unsatisfactory.